Shaped carbon articles are conventionally produced by mixing a finely divided carbonaceous filler and a binder and then molding the mixture into shaped bodies. The carbonaceous filler may be a petroleum or coal coke, pitch coke, powdered graphite, carbon flour or the like. The binder is usually tar or pitch derived from either petroleum or coal. The shaped bodies are then baked at a sufficiently high temperature to carbonize the binder and exclude volatile materials contained therein.
After the shaped bodies have been baked, they are usually impregnated with a liquid pitch and then rebaked again at elevated temperatures in order to reduce their porosity. Depending on the particular application, it may be necessary to impregnate and rebake the shaped bodies several times until the desired porosity and density are achieved. Following the impregnation and rebaking steps, the shaped bodies may be heated to graphitizing temperatures, e.g about 3000.degree. C., in order to produce graphite articles.
This conventional process for producing dense carbon and graphite articles is extremely slow and time-consuming, often requiring five to eight months, to complete the fabrication of relatively large size graphite articles. Unfortunately, the long time periods that are required to fabricate these articles necessitate large inventories and generally make it difficult to respond to the changing needs of customers. In addition, the multiple impregnation and rebaking steps that are employed in the conventional process also require the installation and maintenance of expensive pollution control equipment which also increases the product cost.
U.S. Pat. No. 3,419,645 to Pietzka describes a process for preparing shaped carbon bodies wherein a finely ground coke is blended with a hard pitch, the pitch having a softening point of at least 100.degree. C. The mixture of hard pitch and coke powder is then intimately mixed with a dispersion of colloidal graphite and water and then shaped by means of a press under pressures ranging from 20 to 300 kg/cm.sup.2. After pressing, the shaped bodies are dried at temperatures in the range of from 60.degree. C. to 110.degree. C. The dried pressed bodies may by then either baked to form porous carbon bodies, which may be optionally impregnated, or they may be densified by after-pressing at an elevated temperature, preferably at a temperature in the range of from 30.degree. C. to 50.degree. C. below the softening point of the hard pitch, and subsequently baked to form dense carbon bodies.
French Patent No. 1,587,312 describes a method for producing high density graphite articles wherein a preformed, baked and fully graphitized body is placed in a mold and surrounded by a layer of finely pulverulent, refractory material. The pulverulent material is a poor conductor of heat and electricity e.g. carbon black powder, and is applied around the graphite body to a thickness which is not greater than 10% of the diameter of the body. The body is then heated while surrounded by the pulverent material to a temperature of between 3100.degree. C. and 3650.degree. C. and a static pressure is exerted on the body via the pulverulent material, the pressure being in the range of between 100 and 400 kg/cm.sup.2.
U.S. Pat. No. 3,246,056 to Shea et al. describes surrounding a performed carbonaceous shape with a deformable, pressure transmitting, fluid-impermeable envelope, and applying a pressure to the envelope while heating. The fluid-impermeable envelope contains the gasses generated during heating to prevent formation of voids in the final product.
Lange et al, in an article entitled "The Powder Vehicle Hot-Pressing Technique" published in the Westinghouse Research Laboratory Ceramic Bulletin, Volume 52, No. 7, 1973, describe a hot-pressing technique using a powder vehicle, such as graphite powders, to transfer pressure onto a complex shaped object during densification via an axial stress. The object to be densified is preshaped using a conventional ceramic forming technique, e.g. isostatic pressing, slip casting, injection molding, etc. The object is then embedded in the powder vehicle which is contained within a cylindrically shaped hot-pressing die with end plungers. At the temperature required to densify the preshaped object, a load is applied to the powder vehicle through the end plungers.